:: Bolt On End Caps :: Most injection presses use bolt-on end caps. They are usually constructed from 4140/4150 and have I.D.’s that are generally nitrided or chrome plated. Concor has developed a method of installing a through-hardened “insert” in the angled section of the I.D. to give the end cap better wear resistance. This insert can be installed on a new end cap or a worn one. Minor design changes are occasionally necessary.